1. Description of the Prior Art
FIGS. 3 and 4 illustrate two prior art motor driven fluid compressors. The operation of each of the prior art compressors is well known in the art so that an explanation thereof is omitted.
FIG. 3 illustrates one motor driven fluid compressor having the compression and drive mechanisms within a hermetically sealed housing as disclosed in Japanese Utility Model Application Publication No. 63-105780.
With reference to FIG. 3, compressor 200 includes hermetically sealed housing 210 which contains a compression mechanism, such as scroll type fluid compression mechanism 220 and drive mechanism 230 therein. Housing 210 includes cylindrical portion 210a, and first and second cup-shaped portions 210b and 210c. An opening end of first cup-shaped portion 210b is hermetically connected to an upper opening end of cylindrical portion 210a by, for example, brazing. An opening end of second cup-shaped portion 210c is hermetically connected to a lower opening end of cylindrical portion 210a by, for example, brazing.
Scroll type fluid compression mechanism 220 includes fixed scroll 221 having circular end plate 221a and spiral element 221b which downwardly extends from circular end plate 221a. Circular end plate 221a of fixed scroll 221 is fixedly disposed within first cup-shaped portion 210b by, for example, forcible insertion. First inner block 240 is fixedly disposed within an upper region of cylindrical portion 210a by, for example, forcible insertion and is fixedly connected to circular end plate 221a of fixed scroll 221 by a plurality of bolts 250. Scroll type fluid compression mechanism 220 further includes orbiting scroll 222 having circular end plate 222a and spiral element 222b which upwardly extends from circular end plate 222a. Spiral element 221b of fixed scroll 221 interfits with spiral element 222b of orbiting scroll 222 with an annular and radial offset. Circular end plate 222a of orbiting scroll 222 is radially slidably disposed on an upper end surface of first inner block 240.
Drive mechanism 230 includes drive shaft 231 and motor 232 surrounding drive shaft 231. Drive shaft 231 includes pin member 231a which upwardly extends from and is integral with an upper end of drive shaft 231. The axis of pin member 231a is offset from the axis of drive shaft 231, and pin member 231a is operatively connected to circular end plate 222a of orbiting scroll 222. Rotation preventing mechanism 260 is disposed between first inner block 240 and circular end plate 222a of orbiting scroll 222 so that orbiting scroll 222 only orbits during rotation of drive shaft 231. First inner block 240 includes first central opening 241 within which bearing 270 is fixedly disposed so as to rotatably support an upper end portion of drive shaft 231.
Second inner block 280 axially spaced from first inner block 240 is fixedly disposed within a lower region of cylindrical portion 210a of housing 210 by, for example, forcible insertion. Second inner block 280 includes second central opening 281 within which bearing 290 is fixedly disposed so as to rotatably support a lower end portion of drive shaft 231. Motor 232 includes annular-shaped rotor 232a fixedly surrounding an exterior surface of drive shaft 231 and annular-shaped stator 232b surrounding rotor 232a with a radial air gap. Stator 232b are fixedly sandwiched by first and second inner blocks 240 and 280.
In this prior art compressor, first and second inner blocks 240 and 280 and cylindrical portion 210a of housing 210 are separately prepared before assembling the compressor. Therefore, as far as the above elements are prepared by a normal precise machining manner, it is difficult to obtain the compressor where the longitudinal axis of first central opening 241 of first inner block 240 and the longitudinal axis of second central opening 281 of second inner block 280, and the longitudinal axis of drive shaft 231 and the longitudinal axis of cylindrical portion 210a of housing 210 are easily and precisely aligned. Therefore, an exterior surface of drive shaft 231 non-uniformly contacts to an inner peripheral surface of the inner ring of bearings 270 and 290, thereby causing fragmentation of the exterior surface of drive shaft 231 and damage of bearings 270 and 290 during operation of the compressor. This impulse alignment causes malfunction of the compressor. Furthermore, a non-uniform radial air gap is created between rotor 232a and stator 232b of motor 232, thereby causing a decrease in efficiency of motor 232.
The above-mentioned defects may be resolved, if highly precise machining and assembling manners are used in the manufacturing process of the compressor. However, this requires a complicated manufacturing process of the compressor, thereby increasing manufacturing costs.
In order to resolve the aforementioned defects without providing a complicated manufacturing process of the compressor and increasing the manufacturing costs, Japanese Patent Application Publication No. 1-237376 discloses another motor driven fluid compressor having the compression and drive mechanisms within a hermetically sealed housing as illustrated in FIG. 4. In the drawing, the same numerals are used to denote the substantially the same elements shown in FIG. 3.
With reference to FIG. 4, compressor 300 includes inner block 340 having generally circular disc-shaped portion 341 which is fixedly disposed within cylindrical portion 210a of housing 210 by, for example, forcible insertion. Inner block 340 includes central bore 342 formed through circular disc-shaped portion 341. Annular projection 343 downwardly projects from a lower peripheral end surface of a central bore 342, and terminates at a location which is a midway of cylindrical portion 210a. A plurality of curved plate-shaped projections 344 downwardly project from the lower end surface of a peripheral region of circular disc-shaped portion 341, and terminate at a location which is the midway of cylindrical portion 210a.
An upper end portion of drive shaft 231 passes through central bore 342 and annular projection 343, and is rotatably supported by bearing 270 fixedly disposed within central bore 342 and a pair of plain bearings 343a and 343b fixedly disposed within annular projection 343. Annular-shaped rotor 232a fixedly surrounds an exterior surface of drive shaft 231. Annular stator 232b of motor 232 is fixedly connected to curved plate-shaped projections 344 by a plurality of corresponding bolts 345.
In this prior art compressor, drive shaft 231 is rotatably and solely supported by inner block 340. Therefore, even though an axial length of central bore 342 of inner block 340 is relatively large, the excessive radial thrust force acts on bearings 270, 343a and 343b in a severe operating condition of the compressor in comparison with the prior art compressor shown in FIG. 3 where bearings 270 and 290 are axially spaced from each other with a sufficiently long distance. This severe operating coalition causes unfavorable abrasion of bearings 270, 343a and 343b, thereby decreasing the life thereof.